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In California residential, when is a common trip breaker required as opposed to a handle tied breaker?

The code appears to permit handle-tied breakers for MWBC and also line-to-line circuits.... This seems mostly comprehensive?

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I can point out as far as NEC 240.15(B)(2) the direct quote is, "shall be permitted as the protection for each ungrounded conductor for line-to-line connected loads". So if you connect an electric clothes dryer with the typical 120 VAC tumbler motor, it is not a "line-to-line connected load" and would require a common trip circuit breaker. I could see that applying to the electronics board and clock inside an electric range as well. Any kind of subpanel feeder or backfeed breaker supplying line-to-neutral loads... probably some others too. Basically, anything involving a neutral wire, other than a MWBC, is going to need to be common trip.

There's also an exception to the exception. Now that most residential MWBC locations require AFCI, you won't be able to use single-pole breakers for those either. *see comments

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  • You can now. GE now has AFCIs that don't take neutral, and they market them specifically for MWBCs. Siemens has the same thing but they're tandems so a bit tricky to apply to MWBCs. Oct 5, 2022 at 3:12
  • @Harper-ReinstateMonica so if I have 2 sets of Siemens tandems and find a way to handle tie the middle two switches, then I can have a MWBC without using the 2-pole AFCI? Sneaky. Oct 5, 2022 at 3:22
  • if an approved way, yes. Not sure if Siemens lets you tie tandems, but they'd be fools not to given that feature. You could do a daisy chain of like 6 MWBCs on 7 tandems, long as they're the same ampacity or you don't mind a 15/20 MWBC at one point. Oct 5, 2022 at 3:26
  • @Harper-ReinstateMonica I've got one of their 200 Amp panels and they don't allow more than 5 tandems per side. 😕 Oct 5, 2022 at 3:28
  • That's a CTL thing. It's to prevent you from having >42 throws in the panel. CTL was repealed, so consult Siemens as to what to do there. They may have an answer. Oct 5, 2022 at 3:38
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Your impression is mostly correct. Handle-ties are there to protect maintainers, to assure they turn off the entire circuit and don't get bit by the part they didn't turn off.

Readers: Handle-ties do not grant common trip, because breakers "trip free" - will trip even if held or locked (e.g. fire alarm) in the ON position. So if the handle-tie jammed, the tripping side will trip anyway but will fail to trip the other side. Thus, not usable for common trip. Common trip is an internal mechanism, which is why 2-pole breakers only come from the factory.

(some European DIN Rail breakers expose the common-trip actuating rail, which allows them to build common-trip breakers the same way we build handle-tied breakers. Neat!)

240V-only loads (no neutral) only require handle-ties, not common trip.

120/240V loads (with neutral) require common trip. You can imagine a reason: suppose the dryer motor overheats and trips the breaker on its phase L1. However, L1 is connected to L2 via the heating element, so L1 is still energized, and the motor is still being fed power! However the heating element limits current so the L2 breaker never trips.

MWBCs comprised entirely of 120V loads require handle-ties, not common trip. Tripping one side doesn't affect the other.

MWBCs which contain both 120V and 240V loads (did you know they can do that? They can!) require common trip for the reason illustrated above, except involving multiple appliances.

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